This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for assembling gas turbine engine compressors.
At least some known gas turbine engines include a compressor, a combustor, and at least one turbine coupled in a serial axial-flow relationship. The compressor compresses air which is then channeled to the combustor. The compressed air is mixed with fuel and ignited within the combustor to generate combustion gases which are channeled to the turbine. The turbine extracts energy from the combustion gases to power the compressor, as well as to produce useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Known compressors include a rotor assembly and a stator assembly. The rotor assembly may include a plurality of rotor blades extending radially outward from a shaft. The stator assembly may include a plurality of stator vanes which are coupled between adjacent rows of rotor blades to form a nozzle for directing combustion gases passing therethrough to downstream rotor blades. More specifically, the stator assembly is coupled to the rotor assembly with a fastener assembly or a controlling mass. Maintaining clearances between tips of the rotor blades and the surrounding casing facilitates increasing the operating efficiency of the compressor. However, controlling tip clearances may be difficult because the stationary stator assemblies may thermally expand at a quicker rate than the rotating rotary assembly.
To facilitate controlling flowpath deflection, at least some known compressors use either a split casing, a stacked continuous ring casing, or a continous casing with a segmented flowpath surface coupled to it. Each compressor casing offers advantages and disadvantages. For example, the split casing includes a pair of longitudinally split halves that are bolted together around the rotor assembly. The flowpath surface is then formed after liners are coupled to the split halves. Although the liners insulate the controlled mass from the flowpath, assembly costs are typically higher because of the milling, and pressure deflections and thermal gradients may cause out-of-roundness. In contrast, the stacked continuous ring configuration includes a series of annular rings that are coupled together around the rotor assembly. However, because the flowpath surfaces are integral to the rings, the rings may experience additional thermal growth because they are directly exposed to the flowpath. Within the continuous casing configuration, all of the stator vanes are initially installed around the rotor assembly before a single continuous casing is coupled around them. Each stator vane assembly is then coupled to the casing for retention. Although the controlling mass is insulated from the flowpath, the compressor is much more complicated to assemble, and as such may be more costly than the previously described compressor casing assemblies.